This invention relates to novel styrene derivatives which are useful monomers in preparing base polymers for use in chemically amplified resist compositions for microfabrication.
In the drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The rapid advance toward finer pattern rules is grounded on the development of a projection lens with an increased NA, a resist material with improved performance, and exposure light of a shorter wavelength. In particular, the change-over from i-line (365 nm) to shorter wavelength KrF laser (248 nm) brought about a significant innovation, enabling mass-scale production of 0.18 micron rule devices. To the demand for a resist material with a higher resolution and sensitivity, acid-catalyzed chemical amplification positive working resist materials are effective as disclosed in U.S. Pat. Nos. 4,491,628 and 5,310,619 (JP-B 2-27660 and JP-A 63-27829). They now become predominant resist materials especially adapted for deep UV lithography.
Resist materials adapted for KrF excimer lasers enjoyed early use on the 0.3 micron process, went through the 0.25 micron rule, and currently entered the mass production phase on the 0.18 micron rule. Engineers have started investigation on the 0.15 micron rule, with the trend toward a finer pattern rule being accelerated. A wavelength change-over from KrF to shorter wavelength ArF laser (193 nm) is expected to enable miniaturization of the design rule to 0.13 xcexcm or less. Since conventionally used novolac resins and polyvinylphenol resins have very strong absorption in proximity to 193 nm, they cannot be used as the base resin for resists. To ensure transparency and dry etching resistance, some engineers investigated acrylic and alicyclic (typically cycloolefin) resins as disclosed in JP-A 9-73173, JP-A 10-10739, JP-A 9-230595 and WO 97/33198. With respect to F2 excimer laser (157 nm) which is expected to enable further miniaturization to 0.10 xcexcm or less, more difficulty arises in insuring transparency because it was found that acrylic resins are not transmissive to light at all and those cycloolefin resins having carbonyl bonds have strong absorption.
An object of the invention is to provide a novel styrene derivative which is useful in the preparation of a base polymer for a chemical amplification resist composition having a high transmittance to vacuum ultraviolet radiation of up to 300 nm, especially F2 excimer laser beam (157 nm), Kr2 excimer laser beam (146 nm), KrAr excimer laser beam (134 nm) and Ar2 excimer laser beam (126 nm).
It has been found that a novel styrene derivative of the following general formula (1) can be obtained by the method to be described later, and that using a resin based on a fluorinated polyhydroxystyrene obtained from the novel styrene derivative, a resist composition having transparency and alkali solubility is formulated.
As long as the inventor has confirmed, polyhydroxystyrene is somewhat improved in transmittance near 160 nm, but to an extent far below the practical level, and reducing carbonyl and carbon-to-carbon double bonds is essential for insuring a transmittance. However, phenols are good in etching resistance and alkali solubility, as compared with acrylic compounds. Further, halogen-substituted phenol polymers, and especially fluorine-substituted polymers obtained from the inventive styrene derivatives are improved in transmittance nearly to the practical level.
The invention provides a styrene derivative of the following general formula (1). 
Herein R1 is hydrogen, a straight, branched or cyclic, unsubstituted or fluoro-substituted alkyl group of 1 to 20 carbon atoms, chlorine atom, or trichloromethyl group, R2 is a phenol protecting group, p, q and r are integers in the range of 0xe2x89xa6p less than 5, 0xe2x89xa6q less than 5, 0 less than r less than 5, and 0 less than p+q less than 5.
In formula (1) representative of the novel styrene derivative according to the invention, R1 is hydrogen, a straight, branched or cyclic, unsubstituted or fluoro-substituted alkyl group of 1 to 20 carbon atoms, chlorine atom, or trichloromethyl group. Examples of the straight, branched or cyclic C1-20 alkyl group represented by R1 include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, and n-octyl. The alkyl groups of 1 to 4 carbon atoms are preferred, with methyl being most preferred. The fluorinated alkyl groups are the foregoing alkyl groups in which some or all of the hydrogen atoms are replaced by fluorine atoms, for example, trifluoromethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoropropyl, and 1,1,2,3,3,3-hexafluoropropyl.
R2 is a protective group on a phenol moiety, which is preferably selected from among methyl, vinyl, allyl, benzyl, and groups of the following general formulae (10), (11), (12), (13) and (14). 
In formula (10), R3 is a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms. R4 and R5 each are hydrogen, a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain a hetero atom, R6 is a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain a hetero atom, aryl, aralkyl or oxoalkyl group, and a pair of R4 and R5, a pair of R4 and R6, or a pair of R5 and R6, taken together, may form a cyclic structure of 3 to 12 carbon atoms. R7, R8 and R9 each are a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain a hetero atom, aryl, aralkyl or oxoalkyl group, and a pair of R7 and R8, a pair of R7 and R9, or a pair of R8 and R9, taken together, may form a cyclic structure of 3 to 12 carbon atoms. R10, R11 and R12 each are a straight or branched alkyl group of 1 to 4 carbon atoms. R13 is a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain a hetero atom, aryl, aralkyl or oxoalkyl group, and xe2x80x9caxe2x80x9d is an integer of 0 to 10.
Examples of the alkyl group represented by R3 are the same as exemplified for R1. Alkyl groups of 1 to 4 carbon atoms are preferred, with methyl being most preferred. Illustrative examples of the group of formula (10) are acetyl, propionyl, butyryl and isobutyryl.
In formula (11), examples of the alkyl group represented by R4, R5 and R6 are the same as exemplified for R1. Alkyl groups of 1 to 8 carbon atoms, especially 1 to 6 carbon atoms are preferred. These alkyl groups may contain a hetero atom such as oxygen, sulfur, nitrogen or fluorine. Examples are alkyl groups which are separated by an oxygen atom, sulfur atom or NH group. Also included are alkyl groups in which some or all of the hydrogen atoms are replaced by fluorine atoms.
A pair of R4 and R5, a pair of R4 and R6, or a pair of R5 and R6, taken together, may form a cyclic structure of 3 to 12 carbon atoms, especially 5 to 10 carbon atoms. Each of R4, R5 and R6 is an alkylene group that forms a cyclic structure having the desired number of carbon atoms, when they form a ring.
Illustrative examples of the group of formula (11) are straight or branched acetal groups such as methoxymethyl, methoxyethoxymethyl, 1-methoxyethyl, 1-ethoxyethyl, 1-n-propoxyethyl, 1-isopropoxyethyl, 1-n-butoxyethyl, 1-isobutoxyethyl, 1-sec-butoxyethyl, 1-tert-butoxyethyl, 1-tert-amyloxyethyl, 1-ethoxy-n-propyl, 1-cyclopentyloxyethyl, 1-cyclohexyloxyethyl, 1-methoxy-n-propyl, ethoxypropyl, 1-methoxy-1-methyl-ethyl, and 1-ethoxy-1-methyl-ethyl. These groups are shown by the following formulae. 
Of the groups represented by formula (11), cyclic groups are, for example, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl, tetrahydropyran-2-yl and 2-methyltetrahydropyran-2-yl. Of the groups represented by formula (11), ethoxyethyl, butoxyethyl, and ethoxypropyl are preferred.
In formula (12), examples of the alkyl group represented by R7, R8 and R9 are the same as exemplified for R1. Alkyl groups of 1 to 8 carbon atoms, especially 1 to 6 carbon atoms are preferred. These alkyl groups may contain a hetero atom such as oxygen, sulfur, nitrogen or fluorine. Examples are alkyl groups which are separated by an oxygen atom, sulfur atom or NH group. Also included are alkyl groups in which some or all of the hydrogen atoms are replaced by fluorine atoms.
A pair of R7 and R8, a pair of R7 and R9, or a pair of R8 and R9, taken together, may form a cyclic structure of 3 to 12 carbon atoms, especially 5 to 10 carbon atoms. Each of R7, R8 and R9 is an alkylene group that forms a cyclic structure having the desired number of carbon atoms, when they form a ring.
Illustrative examples of the tertiary alkyl group of formula (12) include tert-butyl, triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl, 1-ethylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, and tert-amyl.
In formula (13), examples of the alkyl group represented by R10, R11 and R12 are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, and tert-butyl. Illustrative examples of the group of formula (13) include trimethylsilyl, triethylsilyl and tert-butyldimethylsilyl.
In formula (14), examples of the alkyl group represented by R13 are the same as exemplified for R1. The hetero atoms which can be contained in these alkyl groups are as exemplified for R4 to R9. Illustrative examples of the group of formula (14) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl, 2-tetrahydropyranyloxycarbonylmethyl, 2-tetrahydrofuranyl-oxycarbonylmethyl, triethylcarbyloxycarbonylmethyl, 1-ethylnorbornyloxycarbonylmethyl, 1-methylcyclohexyloxy-carbonylmethyl, 1-ethylcyclohexyloxycarbonylmethyl, 1-methylcyclopentyloxycarbonylmethyl, 1-ethylcyclopentyl-oxycarbonylmethyl, 2-(2-methyl)adamantyloxycarbonylmethyl, 2-(2-ethyl)adamantyloxycarbonylmethyl, and tert-amyloxy-carbonylmethyl.
Also, R6, R7, R8, R9 and R13 stand for substituted or unsubstituted aryl groups of 6 to 20 carbon atoms, for example, phenyl groups, p-methylphenyl, p-ethylphenyl, and alkoxy-substituted phenyl groups such as p-methoxyphenyl, aralkyl groups of 7 to 20 carbon atoms, such as benzyl and phenethyl. Also included are similar alkyl and other groups having an oxygen atom, similar alkyl and other groups in which a hydrogen atom attached to a carbon atom is replaced by a hydroxyl group, and similar alkyl and other groups in which two hydrogen atoms are replaced by an oxygen atom to form a carbonyl group, as shown below. 
Also R6, R7, R8, R9 and R13 stand for oxoalkyl groups of 4 to 20 carbon atoms, for example, 3-oxoalkyl groups and groups as shown below. 
Referring back to formula (1), p, q and r are integers in the range of 0xe2x89xa6p less than 5, 0xe2x89xa6q less than 5, 0 less than r less than 5, and 0 less than p+q less than 5. The preferred range is qxe2x89xa72, and the more preferred range is q=2 and r=1.
Accordingly, the styrene derivative of the present invention is preferably of the following general formula (2), more preferably of the following general formula (3), and further preferably of the following general formula (4). 
In formula (3), s is an integer in the range of 0 less than s less than 5. 
Of the styrene derivatives, those having the OR2 group at the para position are preferred. Accordingly, the styrene derivatives of the following general formula (5), especially the following general formulae (6) to (8) are preferable. 
Also preferred are those styrene derivatives having the OR2 group at the meta position represented by the following general formula (9). 
The styrene derivative of the invention is generally prepared by cross coupling a benzene derivative of the following general formula (1a) with a vinyl derivative of the following general formula (1b). xe2x80x83CH2xe2x95x90CR1Xxe2x80x83xe2x80x83(1b)
Herein, R1, R2, p, q and r are as defined above, and X is a halogen atom, especially bromo or iodo.
In effecting the cross coupling, organometallic compounds are prepared from the compounds of formula (1a) or (1b), examples of the organometallic compounds including organic lithium compounds, organic magnesium compounds, organic zinc compound, organic copper compounds, organic titanium compounds, organic tin compounds and organic boron compounds. Transition metal catalysts such as palladium, nickel and copper catalysts must be used in the cross coupling. Exemplary palladium catalysts include zero-valent palladium compounds such as tetrakis(triphenylphosphine)-palladium(0) and di(1,2-bis(diphenylphosphino)-ethane)palladium(0), divalent palladium compounds such as palladium acetate, palladium chloride, and [1,1xe2x80x2-bis-(diphenylphosphino)ferrocene]palladium(II) chloride, complexes of the divalent palladium compounds with ligands, and combinations of the divalent palladium compounds with reducing agents.
Exemplary nickel catalysts include divalent nickel compounds such as (1,3-bis(diphenylphosphino)propane)nickel chloride (II), (1,2-bis(diphenylphosphino)ethane)nickel chloride (II), and bis(triphenylphosphine)nickel chloride (II), and zero-valent nickel compounds such as tetrakis-(triphenylphosphine)nickel(0).
Exemplary copper catalysts include monovalent copper salts such as copper (I) chloride, copper (I) bromide, copper (I) iodide, and copper (I) cyanide, divalent copper salts such as copper (II) chloride, copper (II) bromide, copper (II) iodide, copper (II) cyanide, and copper (II) acetate, and copper complexes such as dilithium tetracuprate.
Using the styrene derivative of the invention as a monomer, a polymer or high molecular weight compound is prepared. The polymer is generally prepared by mixing the monomer with a solvent, adding a catalyst thereto, and effecting polymerization reaction while heating or cooling the system if necessary. The polymerization reaction depends on the type of initiator or catalyst, trigger means (including light, heat, radiation and plasma), and polymerization conditions (including temperature, pressure, concentration, solvent, and additives). Commonly used for polymerization the styrene derivative of the invention are radical polymerization of triggering polymerization with radicals of xcex1,xcex1xe2x80x2-azobisisobutyronitrile (AIBN) or the like, and ion (anion) polymerization using catalysts such as alkyl lithium. Such polymerization may be effected in a conventional manner.
The polymer thus obtained is used as a base polymer in formulating a resist composition. The resist composition is generally formulated by adding an organic solvent and a photoacid generator to the polymer. If necessary, a crosslinker, basic compound, dissolution inhibitor and the like are added. The resist composition may be prepared in a conventional way.
The resist composition prepared using a polymer obtained by polymerizing the inventive styrene derivative is sensitive to high-energy radiation, has excellent sensitivity and resolution at a wavelength of up to 200 nm, especially up to 170 nm, and excellent plasma etching resistance. The styrene derivative of the invention is an advantageous raw material for a base polymer for formulating a resist composition having a low absorption at the exposure wavelength of a F2 excimer laser. The resulting resist composition is ideal as a micropatterning material in VLSI fabrication since a finely defined pattern having sidewalls perpendicular to the substrate can easily be formed.